Reference is made to copending U.S. patent application Ser. No. 555,863 filed Nov. 28, 1983 and Ser. No. 555,865 filed Nov. 28, 1983.
The present invention relates to a color television (TV) imaging apparatus which includes a color TV imaging device constructed to generate a multiplex color TV video signal by use of a color separation stripe filter. More particularly, the present invention is concerned with a color TV imaging apparatus of the type having a first bias light supply device for improving color reproducibility in dark scenes and a second bias light supply device for reducing afterimages.
A modern color TV camera employs a color TV imaging device in which a color separation stripe filter is disposed in a photoelectric transducer section to generate multiplex color TV video signals. Typical of such color TV cameras is a single tube type color TV camera which uses as its imaging device an image tube having a photoelectric transducer section with a color separation stripe filter, or a single plate type color TV camera whose imaging device is a solid state image sensor having a photoelectric transducer section with a color separation stripe filter. Because such types of TV cameras are easy to produce in a simple, compact and light-weight construction, various types of products with such capabilities are now in the market.
In a color separation stripe filter of the type described, a plurality of color stripes are arranged in a predetermined repetition mode, at least one kind of the stripes being in a complementary color with respect to a primary color. Generally, a color TV camera comprises a color TV imaging device using the stripe filter to generate a multiplex color TV video signal, and at least two demodulators for producing color signal components by demodulating color signals, or carrier color signals as will be referred to which are contained in an output signal of the imaging device and processed into carriers. The imaging element includes a photoconductive layer in the photoelectric transducer section.
As well known in the art, an undesirable afterimage(image persistence) develops in a color TV imaging device of the type including in a photoelectric transducer section thereof a photoconductive layer which shows a photoelectric phenomenon, a kind of internal photoelectric effects. An expedient heretofore employed to reduce afterimage in such an imaging device is applying bias light in an even distribution to the entire surface of the transducer section. Another problem encountered with a color TV imaging apparatus employing a color separation stripe filter is that color reproducibility is lowered when dark scenes are picked up.
As a result of extended study in search of a solution to the problem of the poor reproducibility, we found that it can be alleviated by supplying bias light to the transducer section of the color TV imaging device in a quantity and at a color temperature which are selected such that the carrier color signals to be demodulated remain greater than the peak-to-peak value of noise applied to demodulators. However, if the quantity and/or color temperature of the bias light is varied with the passage of time, white balance is apt to be destroyed or color reproducibility is apt to be degraded. Further, the bias light should not be of the kind which can not reduce undesirable shading caused by the use of the color separation stripe filter and particularly noticeable in dark scenes.
It is desirable, therefore, that a minimum necessary quantity of bias light be used. Should a large quantity of bias light be selected, the change in the quantity of bias light with the passage of time would also be magnified to pronounce the disturbance in white balance, while the possibility of shading in dark scenes would be increased. However, where a minimum quantity of light required for suppressing deterioration of the color reproducibility in dark scenes is selected for the above reason, the afterimage in the transducer section cannot be favorably reduced. Thus, there has been a keen demand for a solution which reconciles reduction of afterimages and improvement in color reproducibility in dark scenes.